Because of the increasingly wider distribution of Internet, people have increased their dependence on networks accordingly. Thus, the network connection function is one of the indispensable functions for current computers.
Conventionally, referring to FIG. 1, a transformer 110 is electrically connected with a transmitter 120, such as a line driver, and a receiver 130, respectively; wherein, the transmitter not only provides the function of signal transmission, but also handles the impedance matching and the function of providing proper common mode voltage on the cable. Because the computer host must always receive a link pulse to establish the connection, the receiver 130 in the computer host must continuously supply the power. Moreover, because the common mode voltage for the signal on the cable is maintained by the transmitter 120, at this time, it must continuously supply the power to the transmitter 120, otherwise the receiver 130 cannot correctly receive the link pulse.
Furthermore, if the transmitter 120 is turned off to save the power, because the transmitter 120 has been turned off, the input common mode voltage of the receiver 130 will become 0V (volt). Thus, the received signal will be clipped, i.e. clipping, and the output of the turn-off transmitter 120 will be equivalently opened, and the impedance will become indefinite accordingly, which cannot be matched with the characteristic impedance of the cable, and further form the reflection wave. Then, the reflection wave will be mixed with the original signal, and, with the clipping, it will cause the receiver 130 to operate abnormally.
During link-down, because the transmitter 120 must still be supplied with power, the power consumption of the transmitter 120 is quite large. Therefore, the prior art cannot greatly reduce the power consumption of link down stand-by power.